n = int(input())
vlst = list(map(int, input().split()))
dp = [0 for _ in range(n)]
if n == 1:
    print(vlst[0])
    exit()
dp[0] = vlst[0]
dp[1] = max(vlst[1], vlst[0])

for i, v in enumerate(vlst[2:], 2):
    dp[i] = max(dp[i - 2] + v, dp[i - 1])
print(dp[-1])